This invention relates generally to a playback device for retrieving optically recorded signals from a spiral track on a reflective, rotating recording disc, and more particularly to a system permitting rapid access to selected locations on the recording disc.
Advancements in laser technology, and the increasing demand for consumer-affordable video playback equipment, have led to the development of optical recording techniques for recording video and audio signal information. In systems incorporating such techniques, video and audio information is recorded on a continuous spiral track along the surface of a rapidly rotating reflective optical recording disc. During playback, a beam is focused onto the recording track to recover the recorded signal. Appropriate mechanisms and control circuitry assure accurate tracking of the recording track with the focused beam.
Optical recording discs have the advantage of being compact and easily handled. Since no directed mechanical contact with the recording surface is required to retrieve recorded information during playback, optical recording discs exhibit little or mor degradation of signal quality despite numerous playbacks. In addition, the disc format, in contrast to magnetic tape formats, provides convenient access to all parts of a recorded program. This permits optical playback devices to provide such special features as stop-action, slow or fast motion, or reverse action during playback of a recorded program.
Some applications, such as, for example, user-interactive video games with branching functions, require the ability to rapidly locate and display specific portions of the pre-recorded material at separate spaced locations on the disc. In such applications, it is necessary to rapidly and accurately direct the focused beam to the appropriate branch location, or frame, on the disc recording surface. Where it is desired to provide a number of possible branch locations, it is necessary that the playback beam be capable of advancing or retreating multiple frames as quickly as possible.
A system for accurately positioning a beam during playback of an optically recorded program is described in U.S. Pat. No. RE 29,963, incorporated by reference herein. In this system, the optical playback elements are mounted on a sledge, which is radially movable along the undersurface of the recording disc. Radial movement of the sledge provides coarse tracking of the recording track by the playback beam, while instantaneous fine adjustment of the beam position is provided by means of an angularly displaceable mirror in the optical path. While this system permits jumps of one track, as during still frame and slow motion effects, no provision is made for effecting jumps of multiple tracks, as would be desirable to adapt a video disc playback unit for use with, for example video games.